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Influence of Particle Size, Applied Compression, and Substratum Material on Particle-Surface Adhesion Force Using the Centrifuge Technique

FELICETTI, Marcos A.; SALAZAR-BANDA, Giancarlo R.; COURY, Jose R.; AGUIAR, Monica L.
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.15%
The centrifuge technique was used to investigate the influence of particle size, applied compression, and substrate material (stainless steel, glass, Teflon, and poly(vinyl chloride)) on particle-surface adhesion force. For this purpose, phosphatic rock (rho(p) = 3090 kg/m(3)) and manioc starch particles (rho(p) = 1480 kg/m(3)) were used as test particles. A microcentrifuge that reached a maximum rotation speed of 14 000 rpm and which contained specially designed centrifuge tubes was used in the adhesion force measurements. The curves showed that the adhesion force profile followed a normal log distribution. The adhesion force increased linearly with particle size and with the increase of each increment of compression force. The manioc starch particles presented greater adhesion forces than the phosphatic rock particles for all particle sizes studied. The glass substrate showed a higher adherence than the other materials, probably due to its smoother topographic surface roughness in relation to the other substrata.; Brazilian Research Funding Institutions; Capes; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fapesp[06/50692-2]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Método para proteção dos dados contra falhas de comunicação em redes de sensores sem fios.; Method for data protection against communication failures in smart sensors networks.

Ramires Sobrinho, Rubens
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 30/11/2007 PT
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Este trabalho apresenta o desenvolvimento de um método para garantir a proteção dos dados contra falhas de comunicação, em redes de sensores inteligentes sem fios. A rede sem fios foi empregada nos ensaios de modelos físicos reduzidos em centrífuga para estudar o comportamento das âncoras "tartaruga", utilizadas nas linhas de ancoragem de sistemas oceânicos para produção de óleo e gás em águas profundas. O emprego da tecnologia de redes de sensores sem fios tem aumentado em muitas áreas da sociedade, principalmente na engenharia. Dessa forma, muitos problemas estão sendo enfrentados e estudados pelos pesquisadores. Sobretudo no que diz respeito à interferência ambiental, relação de potência e alcance, integridade da informação, miniaturização dos dispositivos, autonomia de energia, limitação de algoritmos e vida útil. A inserção da tecnologia de redes de sensores inteligentes sem fios nos ensaios de modelos físicos reduzidos em centrífuga, além de ser inédita no Brasil, permitirá avanços significativos na determinação de parâmetros que, atualmente, são de difícil obtenção com tecnologias convencionais como os sistemas de aquisição de dados e controle que utilizam cabos e fios. Muitas vezes depara-se com a inconveniência do peso dos cabos e dificuldades de instalação dos dispositivos nos modelos...

Detection of outliers in a gas centrifuge experimental data

Andrade,M. C. V.; Nascimento,C. A. O.; Migliavacca,S. C. P.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2005 EN
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Isotope separation with a gas centrifuge is a very complex process. Development and optimization of a gas centrifuge requires experimentation. These data contain experimental errors, and like other experimental data, there may be some gross errors, also known as outliers. The detection of outliers in gas centrifuge experimental data is quite complicated because there is not enough repetition for precise statistical determination and the physical equations may be applied only to control of the mass flow. Moreover, the concentrations are poorly predicted by phenomenological models. This paper presents the application of a three-layer feed-forward neural network to the detection of outliers in analysis of performed on a very extensive experiment.

Steady-state force-velocity relation in the ATP-dependent sliding movement of myosin-coated beads on actin cables in vitro studied with a centrifuge microscope.

Oiwa, K; Chaen, S; Kamitsubo, E; Shimmen, T; Sugi, H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1990 EN
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To eliminate the gap between the biochemistry of actomyosin in solution and the physiology of contracting muscle, we developed an in vitro force-movement assay system in which the steady-state force-velocity relation in the actin-myosin interaction can be studied. The assay system consists of the internodal cells of an alga, Nitellopsis obtusa, containing well-organized actin filament arrays (actin cables); tosyl-activated polystyrene beads (diameter, 2.8 microns; specific gravity, 1.3) coated with skeletal muscle myosin; and a centrifuge microscope equipped with a stroboscopic light source and a video system. The internodal cell preparation was mounted on the rotor of the centrifuge microscope, so that centrifugal forces were applied to the myosin-coated beads moving along the actin cables in the presence of ATP. Under constant centrifugal forces directed opposite to the bead movement ("positive" loads), the beads continued to move with constant velocities, which decreased with increasing centrifugal forces. The steady-state force-velocity curve thus obtained was analogous to the double-hyperbolic force-velocity curve of single muscle fibers. The unloaded velocity of bead movement was 1.6-3.6 microns/s (20-23 degrees C), while the maximum "isometric" force generated by the myosin molecules on the bead was 1.9-39 pN. If...

Concentrated gram stain smears prepared with a cytospin centrifuge.

Shanholtzer, C J; Schaper, P J; Peterson, L R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1982 EN
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A Cytospin slide centrifuge was used to concentrate 0.05- to 0.5-ml samples of cerebrospinal and other body fluids for Gram stain. Trials with cerebrospinal fluid containing known numbers of microorganisms indicated that the Cytospin increased the sensitivity of cerebrospinal fluid Gram stains by up to 2 logs compared with unconcentrated and conventional centrifuge smears. Cytospin-concentrated smears were prospectively compared with unconcentrated Gram-stained smears and bacteriological culture results for 80 clinical body fluid specimens. Bacteria were seen in unconcentrated smears of 9 of the 16 (56%) fluids which were infected, whereas Cytospin smears of 12 of the 16 (75%) showed bacteria. Cytospin smears revealed more bacteria and demonstrated better leukocyte morphology than did unconcentrated or conventionally centrifuged samples of small volumes of infected body fluids, allowing early diagnosis of infection.

Kinesin force generation measured using a centrifuge microscope sperm-gliding motility assay.

Hall, K; Cole, D; Yeh, Y; Baskin, R J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1996 EN
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To measure force generation and characterize the relationship between force and velocity in kinesin-driven motility we have developed a centrifuge microscope sperm-gliding motility assay. The average (extrapolated) value of maximum isometric force at low kinesin density was 0.90 +/- 0.14 pN. Furthermore, in the experiments at low kinesin density, sperm pulled off before stall at forces between 0.40 and 0.75 pN. To further characterize our kinesin-demembranated sperm assay we estimated maximum isometric force using a laser trap-based assay. At low kinesin density, 4.34 +/- 1.5 pN was the maximum force. Using values of axoneme stiffness available from other studies, we concluded that, in our centrifuge microscope-based assay, a sperm axoneme functions as a lever arm, magnifying the centrifugal force and leading to pull-off before stall. In addition, drag of the distal portion of the axoneme is increased by the centrifugal force (because the axoneme is rotated into closer proximity to the glass surface) and represents an additional force that the kinesin motor must overcome.

Transport Phenomena in Zonal Centrifuge Rotors: I. Velocity and Shear-Stress Distributions of Fluid During Acceleration

Hsu, H. W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1968 EN
Relevância na Pesquisa
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An analysis is presented for the evaluation of velocity components and shear-stress distributions of fluid in zonal centrifuge rotors during acceleration. Analytical expressions for the distribution of tangential and radial velocity components and the tangential shear-stress and the radial shear-stress distributions of fluid are obtained for the transient case. Characteristics of each distribution for a typical density gradient liquid in a zonal centrifuge rotor are computed from the relations derived, and are presented as figures. An unusual phenomenon—the tangential velocity of the gradient exceeding the velocity of the rotor during a particular period of acceleration—is demonstrated.

A HIGH SPEED VACUUM CENTRIFUGE SUITABLE FOR THE STUDY OF FILTERABLE VIRUSES

Bauer, Johannes H.; Pickels, Edward G.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 30/09/1936 EN
Relevância na Pesquisa
27.32%
1. A high speed centrifuge is described in which the speed is limited only by the strength of the material of which the rotor is made. It carries sixteen tubes, each of which conveniently accommodates 7 cc. of fluid. 2. The centrifuge operates in a very high vacuum and therefore requires only a small amount of driving energy. The arrangement has been found to eliminate the possibility of producing injurious frictional heat. 3. The rotating parts are supported by anair-bearing and are driven by compressed air. 4. The centrifuge has been successfully operated at a speed of 30,000 revolutions per minute, representing a maximum centrifugal force in the fluid of 95,000 times gravity. 5 Celluloid tubes used for centrifugation of fluid at high speeds are described. 6. Experiments are described in which good sedimentation of the yellow fever virus was obtained.

SEDIMENTATION IN THE ANGLE CENTRIFUGE

Pickels, Edward G.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/01/1943 EN
Relevância na Pesquisa
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1. Using hemocyanin from Limulus polyphemus as a test material, the process of sedimentation in the angle centrifuge, operating both in vacuum and in the open air, has been investigated. 2. Sedimentation in a given field of force was found less efficient when centrifugation was conducted in the open air, because of thermal convection. 3. Correlations have been made with results obtained in the analytical ultracentrifuge, and a theory of sedimentation in inclined tubes has been presented to explain the experimental results. 4. It has been shown that under proper conditions the angle centrifuge may be used for approximate determinations of particle size. 5. Recommendations, based mostly on experimental evidence, have been made for improving sedimentation and interpreting results. 6. To counteract convective disturbances of either thermal or inertial origin, a satisfactory method has been developed which consists of furnishing the fluid under study with a synthetic density gradient, formed with sucrose or some other non-sedimentable material.

STUDIES ON AGGLUTINATION WITH THE AID OF THE CENTRIFUGE. THE INFLUENCE OF TEMPERATURE ON ABSORPTION AND FLOCCULATION

Gates, Frederick L.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/01/1922 EN
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27.15%
The flocculation of bacteria which have absorbed specific agglutinins may be mechanically effected by means of the centrifuge, with results that coincide with those obtained by the standard method of test. Specific serological differences between meningococci, for example, may be determined by the centrifuge method. The technique is described. By the elimination of the inconstant time factor in the flocculation phase opportunity is given for a closer analysis of specific absorption, and of the influence of various conditions upon both phases of agglutination. The velocity of the absorption reaction is a function of the temperature at which it occurs, and the acceleration with increasing temperature is of the order of chemical phenomena. The absorption reaction proceeds most rapidly near the temperature of antibody destruction. The injurious effect of high temperature is revealed first in the serum; the antigen-antibody complex is not less sensitive. The flocculation phase is also promoted by higher temperature, but lags far behind absorption, and consumes most of the time required for spontaneous agglutination. The presence of an excess of antibodies greatly accelerates absorption and flocculation. The absorption reaction, under such circumstances...

Comparative Efficiency of the Fenwick Can and Schuiling Centrifuge in Extracting Nematode Cysts from Different Soil Types

Bellvert, Joaquim; Crombie, Kieran; Horgan, Finbarr G.
Fonte: The Society of Nematologists Publicador: The Society of Nematologists
Tipo: Artigo de Revista Científica
Publicado em /03/2008 EN
Relevância na Pesquisa
27.15%
The Fenwick can and Schuiling centrifuge are widely used to extract nematode cysts from soil samples. The comparative efficiencies of these two methods during cyst extraction have not been determined for different soil types under different cyst densities. Such information is vital for statutory laboratories that must choose a method for routine, high-throughput soil monitoring. In this study, samples of different soil types seeded with varying densities of potato cyst nematode (Globodera rostochiensis) cysts were processed using both methods. In one experiment, with 200 ml samples, recovery was similar between methods. In a second experiment with 500 ml samples, cyst recovery was higher using the Schuiling centrifuge. For each method and soil type, cyst extraction efficiency was similar across all densities tested. Extraction was efficient from pure sand (Fenwick 72%, Schuiling 84%) and naturally sandy soils (Fenwick 62%, Schuiling 73%), but was significantly less efficient from clay-soil (Fenwick 42%, Schuiling 44%) and peat-soil with high organic matter content (Fenwick 35%, Schuiling 33%). Residual moisture (<10% w/w) in samples prior to analyses reduced extraction efficiency, particularly for sand and sandy soils. For each soil type and method...

Whole-Motion Model of Perception during Forward- and Backward-Facing Centrifuge Runs

Holly, Jan E.; Vrublevskis, Arturs; Carlson, Lindsay E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
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27.15%
Illusory perceptions of motion and orientation arise during human centrifuge runs without vision. Asymmetries have been found between acceleration and deceleration, and between forward-facing and backward-facing runs. Perceived roll tilt has been studied extensively during upright fixed-carriage centrifuge runs, and other components have been studied to a lesser extent.

Compact type-I coil planet centrifuge for counter-current chromatography

Yang, Yi; Gu, Dongyu; Liu, Yongqiang; Aisa, Haji Akber; Ito, Yoichiro
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.32%
A compact type-I coil planet centrifuge has been developed for performing counter-current chromatography. It has a revolution radius of 10 cm and a column holder height of 5 cm compared with 37 cm and 50 cm in the original prototype, respectively. The reduction in the revolution radius and column length permits application of higher revolution speed and more stable balancing of the rotor which leads us to learn more about its performance and the future potential of type-I coil planet centrifuge. The chromatographic performance of this apparatus was evaluated in terms of retention of the stationary phase (Sf), peak resolution (Rs), theoretical plate (N) and peak retention time (tR). The results of the experiment indicated that increasing the revolution speed slightly improved both the retention of the stationary phase and the peak resolution while the separation time is remarkably shortened to yield an excellent peak resolution at a revolution speed of 800 rpm. With a 12 ml capacity coiled column, DNP-glu, DNP-β-ala and DNP-ala were resolved at Rs of 2.75 and 2.16 within 90 min at a flow rate of 0.4 ml/min. We believe that the compact type-I coil planet centrifuge has a high analytical potential.

Human Vestibular Response During 3 Gz Centrifuge Stimulation.

McGrath, R. J.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
27.32%
Approved for public release, distribution unlimited; The use of centrifuges in training aircrew to avoid GLOC is increasing. The purpose of this study was to record the vestibulo-ocular reflex (VOR) and subjective sensations to gain insight into reports of asymmetrical disorientation and disturbance during acceleration and deceleration of GLOC training centrifuges. Horizontal and vertical eye movements and post run sensations were recorded from 15 naive male human subjects seated head erect in a 20.5-ft radius pendulous chair centrifuge. Centrifuge profile was acceleration from 1 to 3 Gz in 19 s, 5 min of sustained 3 Gz, and deceleration to 1 Gz in 19 s. Tests were repeated up to three times with the subject facing the motion, and three times with the subject's back to the motion. Eye position was recorded in the dark using an ISCAN infrared video system. Six subjects experienced GLOC, and 1 withdrew due to unrelated sickness. Slow phase velocity (SPV) and sensations from the 8 subjects who completed all 6 runs were analyzed. Roll of the chair during acceleration and deceleration produced strong pitch, roll, and yaw sensations and eye movements attributable to vestibular Coriolis stimulation. Subjective pitch amplitude change was consistently greater during deceleration than acceleration...

Separative power of an optimised concurrent gas centrifuge

Bogovalov, S. V.; Borman, V. D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/06/2015
Relevância na Pesquisa
27.32%
The problem of separation of uranium isotopes in a concurrent gas centrifuge is solved analytically. Separative power of the optimized concurrent gas centrifuges equals to $\delta U=12.7(V/700~{\rm m/s})^2 (300 ~{\rm K}/T)L, ~{\rm kg ~SWU/yr}$, where $L$ and $V$ are the length and linear velocity of the rotor of the gas centrifuge, $T$ is the temperature. This formula well agrees with an empirical separative power of counter current gas centrifuges. The optimal value of the separative power is not unique on the plane $(p_w,v_z)$, where $p_w$ is pressure at the wall of the rotor and $v_z$ is axial velocity of the gas. This value is constant on a line defined by the equation $p_wv_z=constant$. Equations defining the mass flux and the electric power necessary to support the rotation of the gas centrifuge are obtained.; Comment: 18 pages, 2 figures

Deformation mechanisms beneath shallow foundations

McMahon, Brendan
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
EN
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27.32%
Shallow foundations can provide the most economical solution for supporting small-scale structures. The design approach is quite simple considering the ultimate bearing capacity and working-load settlement. Research has shown that settlement calculations, determined using a linear-elastic approach, usually govern the design but this approach is inappropriate because soil is highly non-linear, even at small strains. The result is that signifi cant discrepancies are observed between predicted and actual settlements. This uncertainty has seen the development of settlement-based approaches such as Mobilisable Strength Design (MSD). MSD uses an assumed undrained mechanism and accounts for soil non-linearity by scaling a triaxial stress-strain curve to make direct predictions of footing load-settlement behaviour. Centrifuge experiments were conducted to investigate the mechanisms governing the settlement of shallow circular foundations on clay and saturated sand models. Clay model tests were performed on soft or rm kaolin beds, depending on its pre-consolidation. Sand model tests were performed on relatively loose Hostun sand saturated with methyl-cellulose to slow consolidation. One-dimensional actuators were developed to apply footing loads through dead-weight or pneumatic loading. A Perspex window in the centrifuge package allowed digital images to be captured of a central cross-section...

Dynamic response of flexible square tunnels: testing and validation of existing design methodologies

Tsinidis, G.; Pitilakis, K.; Madabhushi, G.; Heron, C.
Fonte: ICE Publishing Publicador: ICE Publishing
Tipo: Article; published version
EN
Relevância na Pesquisa
27.32%
This is the final published version. It first appeared at http://www.icevirtuallibrary.com/content/article/10.1680/geot.SIP.15.P.004; A series of dynamic centrifuge tests were performed on a flexible aluminium square tunnel model embedded in Hostun dry sand. The tests were carried out at the centrifuge facility of the University of Cambridge in order to further improve knowledge regarding the seismic response of rectangular embedded structures and to calibrate currently available design methods. The soil?tunnel system response was recorded with an extensive instrumentation array, comprising miniature accelerometers, pressure cells and position sensors in addition to strain gauges, which recorded the tunnel lining internal forces. Tests were numerically analysed by means of full dynamic time history analysis of the coupled soil?tunnel system. Numerical predictions were compared to the experimental data to validate the effectiveness of the numerical modelling. The interpretation of both experimental and numerical results revealed, among other findings: (a) a rocking response of the model tunnel in addition to racking; (b) residual earth pressures on the tunnel side walls; and (c) residual internal forces after shaking, which are amplified with the tunnel's flexibility. Finally...

Theory on Measuring Orientation with MEMS Accelerometers in a Centrifuge

Beemer, Ryan D.; Murali, Madhuri; Biscontin, Giovanna; Aubeny, Charles
Fonte: ASCE Publicador: ASCE
Tipo: Article; accepted version
EN
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This is the author accepted manuscript. The final version is available from ASCE via http://dx.doi.org/10.1061/9780784479087.240; Microelectromechanical systems (MEMS) sensors have become a common part of everyday life and can be found in a number of consumer electronics. Specifically, MEMS accelerometers have become widespread because of their low cost, due to mass production techniques, and ability to sense constant acceleration. This ability allows devices, such as cellular phones, to measure their rotation relative to Earth's gravity. These properties also make MEMS accelerometers an option for measuring the rotation of geo-structures, such as foundations, in the field or in scale model geotechnical centrifuge tests. MEMS accelerometers appear to be especially beneficial for measuring orientation in centrifuge experiments because they are not limited by the design constraints of traditional tilt sensors: a single constant acceleration vector (Earth's gravity). This paper presents the theory behind using single-axis MEMS accelerometers to measure the orientation of an object on a plane of reactive centrifugal acceleration and Earth's gravity within a geotechnical centrifuge. The paper specifically addresses cross-axis sensitivity which can significantly impact measurements and is typically excluded from simpler theories.; The authors acknowledge the National Science Foundation...

Centrifuge scaling considerations for fluid-particle systems

Tan, T.- S.; Scott, R. F.
Fonte: Thomas Telford Ltd. Publicador: Thomas Telford Ltd.
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 01/12/1985
Relevância na Pesquisa
27.32%
Two simulations are involved when a centrifuge is used to test models. First, the behaviour of the model in a uniform ng field is assumed to be similar to that of the prototype. Then the centrifuge is assumed to produce an equivalent ng gravitational field. For most static problems, the centrifuge does produce an equivalent ng gravitational field, but for some dynamic problems involving saturated soil these assumptions can break down. When the soil particles and fluid are moving relative to one another, the behaviour in the ng field is not similar to that in the 1g field unless the Reynolds number in both conditions is less than unity. Since this is a special circumstance, the centrifugal behaviour is not similar to that of the prototype in most cases. To illustrate this, the similarity requirements are examined for a single particle moving in a fluid. If different fluids are used in the model and prototype, then the difference in densities must also be accounted for.

Centrifuge Study of Faulting Effects on Tunnel

Burridge, Paul Brian; Scott, Ronald F.; Hall, John F.
Fonte: ASCE Publicador: ASCE
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 01/07/1989
Relevância na Pesquisa
27.32%
If a tunnel crosses a geological fault which is considered to be active, the possibility of a displacement in the fault must be accounted for in the tunnel design. When the tunnel is embedded in soil, the assessment of the effect of the fault movement is not easy to assess. As a guide to analysis, a series of correctly scaled model experiments in a centrifuge is undertaken. The deflections and stresses induced in a tunnel crossing a fault caused by: (a) Fault displacement; and (b) differential earthquake motions across the fault are quantified by a series of centrifuge tests on a finite length model tunnel. The centrifuge results are used to calibrate a one‐dimensional finite element model of the tunnel for soil‐tunnel interaction effects. The numerical model is then used to predict the response of an essentially infinite length tunnel for design purposes. Bending movements, displacements and shears are displayed. Surprisingly small changes in the bending movements from the finite‐length to the infinite tunnel case are obtained.